This invention is directed to the use of certain well-defined poly(aryl ether surfones) in medical devices where transparency and excellent environmental stress-crack resistance are required. These poly(aryl ether sulfones) are based on 4,4'-dichlorodiphenyl sulfone and 4,4'-biphenol, optionally including one or more additional dihydroxy compounds selected from 4,4'-dihydroxydiphenyl sulfone, hydroquinone and 2,2'bis(4-hydroxyphenyl)propane (bisphenol-A).
Articles made from these poly(aryl ether sulfones) can be stem-sterilized while under stresses of 500 psi or greater, moreover, they are not affected by corrosion-reducing additives such as morpholine, for example. Also, the above materials demonstrate good chemical resistance in contact with commonly used hospital cleaners and detergents.
Poly(aryl ether sulfones) have been known for about two decades. They are tough linear polymers that possess a number of attractive features such as excellent high temperature resistance, good electrical properties, and very good hydrolytic stability. Commercially available poly(aryl ether surfones) include the polycondensation product of 4,4'-dihydroxydiphenyl sulfone with 4,4'-dichlorodiphenyl sulfone, described in, for example, Canadian Patent No. 847,963. The polymer, available from Imperial Chemical Industries, Ltd. contains no aliphatic moieties and has a heat deflection temperature of approximately 210.degree. C. Another commercial poly(aryl ether sulfone), available from Amoco Performance Products, Inc. under the trademark of UDEL .RTM., has a heat deflection temperature of about 180.degree. C. and may be made via the nucleophilic polycondensation of bisphenol-A di-sodium salt with 4,4'-dichiorodiphenyl sulfone, as described in U.S. Pat. No. 4,108,837.
Over the years, there has developed a substantial body of patent and other literature directed to the formation and properties of poly(aryl ether sulfones) and other poly(aryl ethers) (all hereinafter called "PAE"). A broad range of PAE's was achieved by Johnson et al., J. of Polymer Science, A-1, Vol. 5, 1967, pp. 2415-2427; Johnson et al., U.S. Pat. Nos. 4,108,837 and 4,175,175. Johnson et al. show that a very broad range of PAE's can be formed by the nucleophilic aromatic substitution (condensation) reaction of an activated aromatic dihalide and an aromatic diol. By this method, Johnson et al. created a host of new PAE's.
Because of their excellent mechanical and thermal properties, coupled with outstanding hydrolytic stability, the poly(aryl ether sulfones) have been utilized in the medical market for a variety of purposes for at least ten years. These medical devices constitute a wide variety of articles. Obviously, one of the major attributes of these resins that contributes to their wide acceptance for these uses is their ability to be steam autoclaved repeatedly without loss of properties. Steam autoclaving exposes these articles to very severe stresses, and involves repetitive exposures to wet/dry and hot/cold cycles.
Copolymers of 4,4'-dichlorodiphenyl sulfone and 4,4'-dihydroxydiphenyl sulfone together with 4,4'-biphenol are described in British Patent Application No. 2,088,396. The copolymers comprise about 80 to 10 mole percent of repeat units derived from 4,4'-dihydroxydiphenyl sulfone, and correspondingly about 20 to 90 mole percent of repeat units derived from 4,4'-biphenol The application states that the incorporation of the units derived from 4,4'-biphenol into the poly(aryl ether sulfone) yields materials with improved resistance to hot water crazing. The application does not mention steam-sterilizability under load, nor does it teach that the copolymers show resistance to stress-cracking in the presence of boiler additives such as morpholine, or when in contact with typical hospital cleaners and detergents.
Poly(aryl ether sulfones) such as the commercially-available resins described previously show some important deficiencies, particularly in steam sterilization. Parts molded from these materials may stress-crack when stem sterilized under stresses of, say, 500 psi or greater. Where boiler additives such as morpholine are employed to reduce corrosion in the stem generating system or when in contact with commonly used hospital cleaners and detergents, these materials are particularly subject to stress-crack failure. The deficiencies are particularly important when the molded article will be subjected to frequent sterilizations during use, such as in medical storage trays and containers for use in sterilizing and storing medical instruments or the like. Medical appliances, including prostheses, dental appliances, implantable devices and the like wherein prolonged contact with tissue is envisioned, are generally sterilized by alternative means, in part to avoid introducing possible contaminants. In addition, such medical appliances are not subjected to routine cleaning with detergents or the like. Inasmuch as these articles thus ordinarily will not encounter the extreme stresses imposed by cleaning and steam sterilization, the prior art resins generally suffice for these applications.
An improved resin capable of withstanding repeated stem sterilization without stress-cracking or similar failure would thus be an important improvement, particularly for use in the production of steam-sterilizable medical storage trays and containers.